We demonstrated cell imaging without any stain by far-field 2-color infrared (IR) super-resolution microscopy,
combining laser fluorescence microscope and picosecond transient fluorescence detected IR (TFD-IR) spectroscopy.
TFD-IR spectroscopy detects IR absorption by monitoring fluorescence due to an electronic transition from a vibrational
excited level by an additional visible light. By using the IR microscopy based on TFD-IR spectroscopy, the spatial
resolution of the image can be increased to the visible diffraction limit of sub-μm, i.e., the IR is super-resolved. Cell
auto-fluorescence due to flavin molecules was monitored for label-free detection of the cellular components. The
fluorescence image of an A549 cell was obtained by introducing both an IR light at 3300 nm and a visible light at 560
nm. The spatial resolution of the image was estimated to be 1.6 μm. This is about 2.5-times higher resolution than the
diffraction limit of IR light. The fluorescence intensity of the images at 3448 nm was smaller than that at 3300 nm,
corresponding to the smaller IR absorption. Therefore, IR spectral imaging of a single cell was achieved with superresolution.